Field of the Invention
The invention relates to a pump for the conveyance of a fluid with varying viscosity.
Background of the Invention
Frequently very large hydraulic forces are generated in single-stage or multi-stage centrifugal pumps that act in the axial direction, this means in the direction of the longitudinal axis of the shaft of the pump. These forces must be absorbed by the axial bearings of the shaft. However, as these axial bearings have to be made as small as possible for practical and technical reasons it is a well-known measure to provide a balance drum for the compensation of axial thrust acting on the shaft of the pump. This comprises a rotor, typically a substantially cylindrical rotor, rotationally fixedly connected with the shaft and a stator arranged coaxially thereto that is stationary with respect to the pump housing. In this connection the stator can, for example, be configured as a separate sleeve or also be formed by the housing itself. The rotor is dimensioned in such a way that a narrow, ring-shaped relief gap is formed between the rotor and the stator. This, on the high pressure side, is connected to the space behind the impeller and/or having regard to multi-stage pumps to the space behind the last impeller, in such a way that a leakage flow of the conveyed fluid can flow through the relief gap to the low pressure side of the rotor. From there, the fluid is resupplied to the inlet of the pump. Due to the pressure decrease across the rotor, a force is generated in this way in the axial direction which is directed opposite to the hydraulic axial forces generated by the impeller and therefore considerably reduces the forces to be absorbed by the axial bearings.